The present invention relates to methods for deicing roads.
Water purification typically produces a first effluent of relatively “clean water” and a second effluent of “waste water” which includes unwanted contaminates. The softening of hard water by the removal of calcium and magnesium is required for both industrial and household use.
Known water softening processes proceed either by way of ion-exchange, membrane softening or precipitation. In the ion-exchange processes, the calcium (Ca++) and magnesium (Mg++) ions are exchanged for sodium (Na+) and regeneration of the ion-exchange resin is achieved with a large excess of NaCl. This process creates a regeneration effluent that is relatively concentrated aqueous solution of sodium, calcium and magnesium chlorides which has to be discarded.
Alternatively, it is possible to use weak acid resins which exchange hydrogen (H+) for calcium (Ca++) and magnesium (Mg++), and to regenerate the spent resins with a mineral acid. While this method creates less waste water, it is more expensive and yields relatively acidic soft water which is corrosive. Meanwhile, membrane softening concentrates the calcium, magnesium salts and salts of other divalent ions to produce waste waters which require costly disposal techniques.
The precipitation process has traditionally been carried out by the “lime soda” process in which lime is added to hard water to convert water soluble calcium bicarbonate into water insoluble calcium carbonate. This anti-erosion agent process also results in waste water which is difficult to filter.
My previously issued patent, U.S. Pat. No. 5,300,123 (which is incorporated herein by reference), relates to the purification of impure solid salts. Even this process produces salty waste water which must be disposed of.
The disposal of waste water has become an expensive problem for society. For example, approximately 1.61 billion gallons of waste water containing approximately 800,000 tons of mixed sodium, calcium, magnesium chlorides and sulfates is produced from water treatment operations and oil fields in the state of California alone. This waste water must be disposed of, costing the state of California millions of dollars each year. Meanwhile, the disposal of waste water has become even more problematic in other parts of the world.
Accordingly, it would be highly advantageous to provide improved methods deicing roads by use of salty waste waters.
Ironically, though there is an overabundance of waste waters that are contaminated with the salts of Na, K, Ca, Mg, Fe, Cl, SO4, and/or CO3 that, as discussed above, is extraordinarily expensive to dispose of, millions of dollars are spent each year on salts such as sodium chloride for deicing highways. It would thus be advantageous if the salts in waste water could be used for deicing highways.